11-(4-[2-(2-Hydroxyethoxy)ethyl]-1-piperazinyl]dibenzo[b,f]-1,4-thiazepine, is a well established drug substance known under the INN name quetiapine. It is used as its hemifumarate salt having the structure or formula (1)

Quetiapine hemifumarate is a psychoactive compound that is an antagonist for multiple neurotransmitter receptors in the brain. Quetiapine hemifumarate is used as an antipsychotic or neuroleptic. Quetiapine hemifumarate is described, for example, in patent publication U.S. Pat. No. 4,879,288, which describes also the synthesis of quetiapine hemifumarate. Preparation of hemifumarate is described also e.g. in EP 0 282 236, and WO 01/55125. Different polymorphic forms of quetiapine hemifumarate and their preparation are described in WO 03/080065, WO 2004/076431 and WO 04/078735. The crystallization of quetiapine base and its use in the preparation of quetiapine hemifumarate is described in U.S. Pat. No. 6,372,734. There industrial methylated spirit is used as a solvent and it is said that crystalline fumarate salt is obtained in good purity and high yield without by-products of other salts. Anyhow, no information about the purity of the product is given.